The "Snoopy Cap" (or CCA—the little hat that holds the communications headset onto the astronauts’ heads) is nicknamed that because its two-tone design (white in the middle, black on the sides) resembles Snoopy’s head. But why the two-tone design? Why not all white or all black?
It looks like the earliest designs used two fabrics(lycra for the middle, teflon for the sides). But fabric technology has come a long way, and lycra is available in every color of the rainbow now (even if it wasn’t back then—not sure of lycra’s tiemline). Per this NASA page, it looks like it’s still that two-tone design.
Why was it originally Lycra at the top/back and Teflon at the sides?
My sense (WAG) is that the sides were Teflon because of being waterproof (which would benefit the electronics in the pouches), and the top/back was Lycra to aid in wicking scalp sweat away from the hair, making things a bit less uncomfortable for the astronaut.
And having it be two-toned makes it easier to tell when the cap is misaligned and in need of correction (again, WAG).
I would think the stretchiness of the lycra would hold the cap in place properly on the head. If you’re bouncing around on the moon, or turn your head to suddenly, and the cap slips, you’ve got to go to a pressurized environment and take your helmet off to straighten it out.